This thesis aims to analyze the impact of user interface (UI) and user experience (UX) design on children's interaction and engagement while using two different versions: a 3D mobile game and a mobile augmented reality (MAR) game. Both versions will feature interactive scenarios focusing on the ease of controls, navigation, and user engagement. The study will explore how design elements in the 3D and MAR environments influence children's ability to interact with the application effectively, evaluating factors like interface clarity, responsiveness, and user satisfaction. Additionally, the thesis will involve the design of the application's visual style and its implementation, with an emphasis on creating a UI that suits the target group. The visual design will be tailored to the needs of early school-aged children, optimized for both versions, and culminate in a functional prototype for testing. The outcome will compare the usability and engagement levels of both versions, highlighting the role of UI/UX in enhancing user interaction and overall experience.